Glossary Plant Breeding

Gametogenesis. The formation of female and male gametes (sex cells). Oogenesis and
spermatogenesis refer to the formation of egg cell and sperm cell, respectively.
Genotype-Environment Interaction. Thechangeinorder, ranking, andrelativevalues
among genotypes across various environments, which are due primarily to macroenvironmental
differences. If genotypes behave consistently, G-E interaction comes to
zero, and consequently genotypes are judged stable. G-E interactions increase rapidly
even to unmanageable levels with the increase in the number of genotypes,
environments, and the level of classification. In low-input agriculture and/ or low
productivity environments in which most variables are unpredictable, high G-E
interactions are observed. Consequently, identification of superior genotypes becomes
very difficult.
Gametic Frequency. The frequency of a particular kind of gamete in the population. All
the three parameters, viz., gene frequency, genotypic frequency and gametic
frequency, are used to describe genetic variation at a locus (loci).
Gametophyte. The haploid gamete-producing stage in the life cycle of plants. It is
prominent and independent in some species, but reduced or parasitic in others.
Gametophytic Incompatibility. A mating system in which incompatibility reaction is
governed by the genetic constitution of the male gametes. It is also called
oppositional-factor system because stylar tissues prohibit or slow down the growth of
pollen-tube containing the same allele of the incompatibility gene. Although
controlled by one gene with multiple alleles (Nicotiana spp.), two-loci system has
also been found (e.g., rye).
Gene (Johannsen 1909). The fundamental and functional unit of heredity. In classical
sense, any inherited factor that determines a biological characteristic of an organism is
called a gene. The concept of the gene dates back to 1865 when Gregor Mendel
showed that certain well-defined attributes of Pisum spp. are governed independently
by a number of factors (genes). Biochemically, it is a segment of DNA, composed of
a transcribed region and a regulatory sequence that make transcription possible.
Gene Action. The way a gene(s) acts in producing a particular phenotype. It can be linear
or non-linear.
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